The present invention relates to the field of downhole tools used in oil, gas, geothermal, and horizontal drilling. Moreover, the present invention relates to systems used to actuate such downhole tools. Many such actuation systems include at least one valve. The prior art discloses valves used in downhole actuation systems.
U.S. Pat. No. 5,706,905 to Barr, which is herein incorporated by reference for all that it contains, discloses a modulated bias unit, for use in a steerable rotary drilling system, of the kind including at least one hydraulic actuator, at the periphery of the unit, having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled, and a control valve operable to bring the actuator alternately into and out of communication with a source of fluid under pressure. The control valve is operable between a first position where it permits the control valve to pass a maximum supply of fluid under pressure to the hydraulic actuator, and a second position where it prevents the control valve from passing said maximum supply of fluid under pressure to the hydraulic actuator. The control valve may include two relatively rotatable parts comprising a first part having an inlet aperture in communication with said source of fluid under pressure and a second part having at least one outlet aperture in communication with said hydraulic actuator. The said inlet aperture, in use, is brought successively into and out of communication with said outlet aperture on relative rotation between said valve parts. The said control valve may be a disc valve wherein said relatively rotatable parts comprise two contiguous coaxial discs.
U.S. Pat. No. 5,133,386 to Magee, which is herein incorporated by reference for all that it contains, discloses a hydraulic servovalve controlled electrically through electromagnetic means. Electrical currents applied to force motors determine the relative position, displaceable control assembly within the valve. Displacive movement of the control assembly changes, in reciprocal proportion, the inlet and outlet flow-metering clearances in each of the chambers of this open-passage type valve. The position of the control assembly determines the inlet and outlet flows within, and, therefore, the net flow through, each chamber. Moreover, since the chambers are each connected (either directly, or through a flow-impeding orifice) to one of the control ports, the position of the control assembly thereby determines the control flow delivered by the valve. Generally, both hydrostatic and hydrodynamic forces within the valve are balanced against corresponding forces, all acting upon the control assembly. However, any internal unbalanced hydrodynamic forces—which arise in proportion to control flow—are compensated by opposing hydrostatic forces, creating a naturally stable servovalve over a wide range of operating conditions.